1. Field of the Invention
The present invention relates to a sheet film package wherein a sheet of photo film is removably packed in a light-shielding envelope.
2. Background Art
A sheet film package contains a relatively large sheet film, e.g. a 12.5.times.10 cm format sheet film, which is mainly directed to professional photography. The light-shielding envelope of the sheet film package has an open end for entrance and exit of the sheet film. The open end is sealed with a clip in a light-tight fashion to prevent ambient light from entering the interior of the light-shielding envelope.
To expose the sheet film, the sheet film package is loaded in a film holder attached to the rear side of a camera. When loading the sheet film package, a lock lever of the film holder is set in a releasing position. Thereafter, the sheet film package is inserted in the film holder with the clip located in the innermost position of the film holder. Then, the lock lever is set in a locking position, thereby holding the clip in the innermost position and, simultaneously, allowing the light-shielding envelope to separate from the clip. Most portion of the light-shielding envelope is then withdrawn from the film holder to leave the sheet film in an exposure position behind an exposure frame of the camera.
After exposure of the sheet film, the light-shielding envelope is moved back into the film holder so as to insert the exposed sheet film therein. Where the sheet film is fully inserted in the light-shielding envelope, the open end is sealed with the clip again by resetting the lock lever to the releasing position. Thus, the sheet film and the light-shielding envelope may be removed together from the film holder by pulling out the light-shielding envelope.
As the sheet film package is a single-use article, the manufacturing cost must be low. Japanese Laid-Open Patent Application No. 4-356039 discloses a sheet film package whose light-shielding envelope is made of paper of about 240 .mu.m thick blackened with carbon. To manufacture the light-shielding envelope of the known sheet film package, two identical paper sheets are mated together and sealed along longitudinal edges with side-sealing tapes, whereas one end is sealed with an adhesive agent. Although the black paper is cheap, this known configuration requires a large amount of side-sealing tape, two taping machines and accurate positioning of the paper sheets, so the material cost and the equipment cost cannot be sufficiently lowered, and the production speed is relatively low.
To solve this problem, it is possible to form a light-shielding envelope by folding a single sheet of paper along a center line and close the opposite side to the folded side with a sealing tape. However, as the side-sealing tapes also serve as reinforcing tapes for preventing the light-shielding envelope from bending, providing the side-sealing tape only along one side can make the light-shielding envelope easy to bend while being inserted into the film holder, especially while being moved back into the film holder after the exposure.